Question

Why does the ammeter have to be connected in series?

Answer 1

An Ammeter is connected in series with the circuit because the purpose of the Ammeter is to measure the current through the circuit.Since the Ammeter is a low impedence device (as ammeters are not supposed to block the current flowing through the circuit affecting the working of the circuit) connecting it in parallel with the circuit would cause a short circuit( as current always follow the low resistive path i.e, ammeter), damaging the Ammeter and/or the circuit.